Our work is broadly concerned with the biochemical basis of microbial pathogenicity. We plan to characterize a series of cytolytic toxins of bacterial origin, particularly those synthesized by staphylococci and streptococci, to elucidate their modes of action, and to evaluate them with respect to their contribution to disease processes. The specificity associated with the biological activities of cytolytic toxins suggests that they may be useful in the investigation of the structure and composition of cell membranes. We therefore plan to study in some detail the effects of several bacterial toxins on membrane ultrastructure.